The inkjet printing method is a printing/recording method whereby ink droplets are directly discharged from a very fine nozzle and deposited onto a base material for printing/recording, to obtain text and images.
The water-based inkjet printing method has traditionally been believed not suitable for the manufacturing of large volumes of printed matters due to such problems as long printing times required by scanning-type print heads, slow drying of water-based media, and so on.
On the other hand, the inkjet printing method has such advantages as not requiring a platemaking process unlike standard printing methods, and enabling printing using equipment of much simpler constitution compared to other methods including the electrophotographic method, and therefore the inkjet printing method has mostly been used in personal and home applications.
In light of the above, the inkjet printing method is worthy enough as a competitor of other printing methods for use in office, commercial printing, and other industrial applications, so long as the aforementioned problems of long printing and drying times can be resolved. For this reason, art of increasing the printing speed and applying low-cost printing paper is actively studied in recent years, from the viewpoints of both printing equipment and ink, with the aim of using the inkjet printing method in industrial applications.
In industrial applications, not only uncoated paper such as inexpensive plain paper and standard offset printing paper, but also low-absorbent media such as coated paper, are being studied for use as base materials for printing. In the case of uncoated paper, ink droplets containing pigment permeate into the uncoated paper the moment they reach the paper, thereby causing the resulting printed matter to lack a feeling of denseness and have a narrow color gamut. In the case of a low-absorbent medium, on the other hand, ink droplets are not easily absorbed into the medium and thus create bleeding on the printed matter. In addition, storage stability, which is an essential performance requirement imposed by the inkjet printing method on inks, must also be offered.
To solve these problems, a method for manufacturing water-based pigment dispersant wherein a pigment, a (meth)acrylic acid ester copolymer, and an organic compound containing glycidyl groups, are dispersed and cross-linked in a water-based medium, is disclosed (refer to Patent Literature 1, for example).
However, the water-based pigment inks containing the aforementioned pigment dispersant could not achieve satisfactory levels of storage stability and color gamut.
Additionally, to solve the aforementioned problems, a water-based inkjet recording ink composition containing inkjet recording crosslinked polymer grains is disclosed, wherein the crosslinked polymer grains contain a colorant, the crosslinked polymer grains are obtained by crosslinking a polymer using a crosslinking agent that contains two or more epoxy groups, and the polymer contains a constitutional unit derived from a direct-chain or branched-chain alkyl group or alkenyl group-containing monomer with 6 to 22 carbon atoms (refer to Patent Literature 2, for example).
According to the Examples in Patent Literature 2, however, the water-based inkjet recording ink composition containing crosslinked polymer grains that in turn contain a constitutional unit derived from stearyl methacrylate by 10% in the polymer, is described as having poorer stability than the water-based inkjet recording ink composition containing crosslinked polymer grains that in turn contain a constitutional unit derived from lauryl methacrylate by 10% in the polymer. Also, the stability of the water-based inkjet recording ink composition containing crosslinked polymer grains that in turn contain a constitutional unit derived from lauryl methacrylate by 10% in the polymer was not yet at a satisfactory level.